The magnetism and electronic structure of the novel hydrogen-bonded coordination polymer [Cu-II(HF2)(-pyz) (2)]BF4 (pyz = pyrazine) is investigated within a series of solid-state hybrid density functional calculations. The optimised crystal structures, strengths of the mu(1,4)-pyz- and weaker mu(1,3)-HF1-- mediated exchange couplings, spin density distributions and electronic densities-of-states are detailed and discussed. A quantum mechanical treatment of the proton motion in the HF2- ions yields no significant variation in magnetic properties. (C) 2008 Elsevier B.V. All rights reserved.